MyFirstObjectWalk: use additional arg in config_fn_t

Commit a4e7e31 (config: add ctx arg to config_fn_t, 2023-06-28)
added a fourth argument to config_fn_t but did not change relevant
function calls in Documentation/MyFirstObjectWalk.txt.

Fix those calls and the example git_walken_config() to use
that additional argument.

Signed-off-by: Dirk Gouders <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dgouders

Documentation/MyFirstObjectWalk.txt

@@ -210,13 +210,14 @@ We'll also need to include the `config.h` header:
 
 ...
 
-static int git_walken_config(const char *var, const char *value, void *cb)
+static int git_walken_config(const char *var, const char *value,
+			     const struct config_context *ctx, void *cb)
 {
 	/*
 	 * For now, we don't have any custom configuration, so fall back to
 	 * the default config.
 	 */
-	return git_default_config(var, value, cb);
+	return git_default_config(var, value, ctx, cb);
 }
 ----
 
@@ -389,10 +390,11 @@ modifying `rev_info.grep_filter`, which is a `struct grep_opt`.
 First some setup. Add `grep_config()` to `git_walken_config()`:
 
 ----
-static int git_walken_config(const char *var, const char *value, void *cb)
+static int git_walken_config(const char *var, const char *value,
+			     const struct config_context *ctx, void *cb)
 {
-	grep_config(var, value, cb);
-	return git_default_config(var, value, cb);
+	grep_config(var, value, ctx, cb);
+	return git_default_config(var, value, ctx, cb);
 }
 ----